The incandescent light bulb has quickly become the most widely applied lighting device in the world since it was invented. The incandescent light bulb is easy to install and can be conveniently powered with either alternating current (AC) or direct current (DC). Therefore, the incandescent light bulb and the screw-type lamp socket therefor are available almost everywhere in the world.
However, due to the progress in the scientific and technological fields, a variety of new and energy-saving lighting devices, such as hot cathode fluorescent lamp (HCFL), cold cathode fluorescent lamp (CCFL) and light-emitting-diode (LED) lamp, has been constantly developed and introduced into market in response to the requirement for energy saving in the modern society. Compared to the new types of energy-saving lighting devices, the conventional incandescent light bulb has high power consumption and low luminous efficiency and fails to satisfy the energy saving requirement.
The newly developed lighting devices respectively have uniquely designed lamp base and socket, and use different and incompatible voltages and frequencies. For instance, the LED lamp uses 3˜5V DC while the CCFL uses current having a voltage as high as several hundred volts. Therefore, these new lighting devices could not be directly used with the conventional screw-type lamp socket that is still used by most people.
According to one of the ways for installing various new types of energy-saving lighting devices on the conventional screw-type lamp socket, a circuit board for regulating voltage and current and a light-emitting element are together packaged in a lamp base. For example, as shown in FIG. 1, to mount a compact fluorescent lamp (CFL) 11 on a general screw-type lamp socket, the tube of the CFL 11 is first formed into a circular or a helical shape and then sealed in a lamp shade 12, and voltage transforming and control circuits 10 are mounted inside a lamp base to thereby form an energy saving lamp that can be conveniently fitted in the existing screw-type lamp socket and has low power consumption. In this type of energy saving lamp, the circuit board is transversely located above the light-emitting element of the lighting device. Heat generated by the light-emitting element is stopped by the transversely mounted circuit board from dissipating into environment outside the lamp base. Therefore, the energy saving lamp as shown in FIG. 1 actually has relatively low heat dissipation efficiency. Further, since an additional procedure is required to weld the circuit board to the lamp base, more time and labor is needed to produce the conventional energy saving lamp while the production efficiency and reliability thereof is reduced.
To reduce the manufacturing cost of the energy saving lamp, US Patent Publication No. 2008/0174224 discloses an improved lamp structure that can be manufactured with simplified procedures to reduce the manufacturing cost and allows convenient inspection and repair of the lamp. For this purpose, the lamp structure includes a lamp base having a base body and a circuit board. The circuit board is fitted in the base body with an electrically conductive layer on lateral edges of the circuit board exposed from openings provided on the base body. Therefore, the lamp structure is simple and easy to produce.
However, the electrically conductive layer is a thin film structure coated on the lateral edges of the circuit board, and accordingly, has low mechanical strength and electrical connection performance compared to the conventional metal-made lamp base. Moreover, to coat the electrically conductive layer on the lateral edges of the circuit board, complicated via plating process is needed and the circuit board must be carefully and precisely cut. These procedures adversely reduce the benefit from the simplified manufacturing procedures.